This invention relates to small PMDC motors and in particular, to the laminations forming the core of the armature for such a motor.
In small PMDC motors, the rotor or armature typically has a laminated core. The laminations are stamped from sheet electrical steel and stacked together to form the armature core which is pressed onto a shaft along with a commutator. The core is then placed in a winding machine where wire, typically enamel coated copper wire is wound about salient poles of the core and terminated on the commutator.
In three pole armatures, the wires are wound around individual poles, where as for armatures with higher number of poles, the windings may be wound about groups of poles.
In individually wound poles, the windings of adjacent poles occupy or share a common winding tunnel which is the space between adjacent poles. For armatures having a high fill rate and/or having fine wire size, the first winding to be wound may fill up the bottom of the winding tunnel spreading into the area which ideally should be occupied by the adjacent winding which is yet to be wound. Thus when the adjacent winding is wound, it is wound, at least partially, on top of the previously wound winding. This leads to a number of problems, including the second winding being larger than the first winding and the last winding is likely to be bigger yet again as it is wound between two adjacent windings. This means that although the number of turns of each winding is the same, the amount of wire used is different as the later windings are wound along a longer path. Thus the resistance of each winding will be different, which for thin and very thin wires can have an adverse effect on motor performance. Also, the greater volume of wire means that the windings are not the same weight, leading to a problem in balancing the motor, i.e., if the armature core is almost balanced before winding, after winding the armature will be significantly out of balance and when automated balancing machines are used to balance the armature, this may have an adverse effect on performance as the automatic balancing machines operate on a material removal principle and remove material from the armature core to balance the armature. The more material that is removed from the core, the bigger the effect on performance. Another important consideration, in the balance of the armature, is the radial positioning of the coils. If this is not the same, the dynamic balance of the armature will be adversely affected. By radial positioning we mean the radial distance between the axis of the armature to the center of mass of the coil. Differences in this distance between the coils of an armature will affect the dynamic balance of the armature leading to vibration in use if not corrected.
Thus it is an object of the present invention to provide a lamination for an armature which can be wound using a winding machine which provides for separation of windings about individual poles of the armature, in a simple yet effective manner.